A pawn structure is the arrangement of the pawns, especially in the centre. It helps you predict which files may open, which squares can become outposts, and which pieces need better routes. Because pawns cannot move backwards, a pawn exchange or advance often changes the character of a position more permanently than a piece move.
The French Advance offers a clear example. After 1.e4 e6 2.d4 d5 3.e5, White has a chain pointing towards the kingside. Black's 3...c5 attacks d4, the supporting base of that chain. White often reinforces it with c3. Black can then increase pressure with ...Nc6 and ...Qb6. These moves form a coordinated plan rather than a collection of developing moves.
Look for pawn breaks: advances that challenge an opposing pawn and create the possibility of an exchange. In this structure, ...c5 and a later ...f6 are important Black ideas. Their timing depends on development and king safety. Playing a thematic break before your pieces are ready may open lines for the opponent instead.
When studying a new opening, keep one diagram of its characteristic structure. Note the likely breaks, the least active piece for each side, and the files that could open. Then compare a model game with your own games. Do not label doubled or isolated pawns as automatically bad: their weaknesses must be weighed against activity, space and concrete threats in the actual position.
Try this at the board
After ...c5, explain why supporting d4 can matter even though White's most advanced pawn is on e5.